1. Field of the Invention
The present invention relates to a drive circuit for driving a switching element in, for example, a switching power source apparatus.
2. Description of Related Art
An example of a switching power source apparatus is described in Japanese Unexamined Patent Application Publication No. H04-105552 (Patent Document 1). This apparatus connects a primary winding of a transformer and a switching element, which is a MOSFET, in series to both ends of a DC power source. The apparatus turns on/off the switching element to generate an AC voltage on a secondary winding of the transformer. The AC voltage on the secondary winding is rectified and smoothed with a first rectifying-smoothing circuit into a DC output voltage, which is supplied to a load.
The DC output voltage is fed back through, for example, a photocoupler to a controller on the primary side of the transformer. Based on the fed-back voltage, the controller controls the switching frequency of the switching element in such a way as to bring the DC output voltage to a target value.
The transformer is provided with an auxiliary winding to generate an AC voltage, which is rectified and smoothed with a second rectifying-smoothing circuit into a DC voltage and is supplied as a control power source to the controller that is a part of the drive circuit. The controller is driven by the control power source and outputs a pulse signal according to which the drive circuit turns on/off the switching element.